Backpack

FIG. 1 is a front, left and top perspective view of a backpack, showing my new design. FIG. 2 is a rear, right and bottom perspective view thereof. FIG. 3 is a front elevation view thereof. FIG. 4 is a rear elevation view thereof. FIG. 5 is a left side elevation view thereof. FIG. 6 is a right side elevation view thereof. FIG. 7 is a top plan view thereof. FIG. 8 is a bottom plan view thereof. FIG. 9 is an enlarged view of detail 9 in FIG. 1 . FIG. 10 is an enlarged view of detail 10 in FIG. 1 . FIG. 11 is an enlarged view of detail 11 in FIG. 2 ; and, FIG. 12 is an enlarged view of detail 12 in FIG. 2 . The dashed broken lines depict portions of the backpack that form no part of the claimed design. The dot-dash broken lines in FIGS. 1 - 2 and 9 - 12 depict the boundaries of the enlarged views and form no part of the claimed design. The dash-dot-dot-dash broken lines depict stitching that form no part of the claimed design.